Locks of the general type to which this invention is directed have at least one tumbler in the form of a lever mounted for turning movement about a pivot when the tumbler is engaged by the lift of a cut key. To withdraw the bolt and open the lock, the tumbler must be turned by the key through a precise angle about its pivot, such that a gate or notch formed in the tumbler is aligned with a so-called "racking bar" on the bolt, or with a "comb" that moves with the bolt. If the gate of a tumbler is disaligned with the racking bar or comb, that tumbler blocks withdrawal of the bolt; if all the gates are aligned, they receive the racking bar or comb and permit the bolt to be withdrawn. In such locks the "shape" of the key, or more precisely, the heights of the respective lifts of the key, control the positions to which the tumblers are turned by rotation of the key; or conversely, the positions at which the tumbler gates are aligned control the shape of the key. In order to set the lock for opening by a particular key, or to reset it to a different key, it is necessary to change the degree of rotary movement which brings one or more of the tumblers into position of gate alignment.